Moraxella catarrhalis (also known a Branhamella catarrhalis) is an important human respiratory tract pathogen. M. catarrhalis is the third most common cause of otitis media in infants and children, after Streptococcus pneumoniae and nontypeable Haemophilus influenzae, as documented in studies in which tympanocentesis has been used to establish the etiologic agent (Murphy, 1989, Pediatr. Infect. Dis. J. 8:S75-S77). M. catarrhalis is a common cause of sinusitis and conjunctivitis in both children and adults (See for example, Bluestone, 1986, Drugs 31:S132-S141; Brorson et al., 1976, Scand. J. Infect. Dis. 8:151-155; and Romberger et al., 1987, South. Med. J. 80:926-928); and is an important cause of lower respiratory tract infections in adults with chronic bronchitis and chronic obstructive pulmonary disease (Murphy et al., 1992, Am. Rev. Respir. Dis. 146:1067-1083; Catlin, 1990, Clin. Microbiol. Rev. 3:293-320). Additionally, M. catarrhalis can cause pneumonia, endocarditis, septicemia, and meningitis in immunocompromised hosts (Cocchi et al., 1968, Acta Paediatr. Scand. 57:451-3; Douer et al., 1977, Ann. Intern. Med. 86:116-119; McNeely et al., 1976, Am. Rev. Respir. Dis. 114:399-402).
Since recurrent otitis media is associated with substantial morbidity, there is interest in identifying strategies for preventing these infections. One such approach is the development of vaccines. An effective vaccine for preventing bacterial otitis media would need to include antigens which would generate protection against infection by S. pneumoniae, non-typeable H. influenzae and M. catarrhalis. Indeed, vaccine development for the pneumococcus and nontypeable H. influenzae are progressing such that potentially protective antigens have been identified and are currently undergoing testing (See for example, Murphy et al., U.S. Pat. No. 5,173,294; and Vella et al., 1992, Infect. Immun. 60:4977-4983). As these vaccines are developed and used more widely, the relative importance of M. catarrhalis as a cause of otitis media will increase in the next decade. Besides infants and children benefitting from a vaccine to prevent otitis media caused by M. catarrhalis, adults with chronic obstructive pulmonary disease, and immunocompromised children and adults would benefit from a vaccine to prevent infections caused by M. catarrhalis.
Bacterial components which have been investigated as potential vaccine antigens include polysaccharides, lipopolysaccharides or modifications thereof, and outer membrane proteins. In general, as exemplified by the type b capsular polysaccharide of H. influenzae, polysaccharide antigens have been shown to be a poor immunogen in children under the age of 18 months. Active immunization with lipopolysaccharide (LPS) is unacceptable due to its inherent toxicity. The pathophysiologic effects of LPS may include fever, leucopenia, leucocytosis, the Shwartzman reaction, disseminated intravascular coagulation, and in large doses, shock and death. In general, proteins are immunogenic in infants around three months of age. Thus, outer membrane proteins are being investigated as possible vaccine antigens.
While recent studies have begun to focus on outer membrane proteins of M. catarrhalis, little is known about the antigenic and molecular structure of these proteins. Studies of purified outer membranes by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) have revealed a rather homogeneous pattern among strains of the bacterium (Bartos and Murphy, 1988, J. Infect. Dis. 158:761-765). At least eight major outer membrane proteins, designated by the letters A-H, have been identified (Murphy et al., 1989, Microbial Pathogen. 6:159-174; Bartos et al., 1988, J. Infect. Dis. 158: 761-765). Experiments in which 20 strains of M. catarrhalis were absorbed with antisera developed against M. catarrhalis strain 25240 indicate that outer membrane protein E contains antigenically conserved determinants that are expressed on the bacterial surface (Murphy et al., 1989, Infect. Immun. 57:2938-2941).
Hence, with the increasing recognition of M. catarrhalis as an important bacterial pathogen, there is a need for a vaccine that is immunogenic in children and adults. Such a vaccine would have to be directed to a bacterial component which has a surface-exposed epitope on intact bacteria, wherein the epitope is conserved amongst strains of M. catarrhalis.